This invention relates to frothed gels containing synthetic mica crystals, to a procedure for effecting ion exchange in such gels, and especially to cellular ceramic bodies produced from such ion-exchanged gels. It is particularly concerned with the exchange of large cations (such as potassium ions) for sodium or lithium ions in a gel formed from a water-swelling mica (e.g., a lithium fluorhectorite gel) to produce such ion-exchanged gels. The resulting gels tend to set in a rapid, but controllable, manner.
U.S. Pat. No. 4,239,519 (Beall et al.) describes the formation of crystal-containing gels and the fabrication of papers, boards, fibers, films, and coatings from those gels. The process for preparing the gels contemplates three basic steps:
(1) a fully or predominantly crystalline body is formed (commonly a glass-ceramic body) containing crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally-compatible species selected from the group of talc, fluortalc, fluorpolylithionite, polylithionite, phlogopite, and fluorphlogopite;
(2) the body is contacted with a polar liquid, normally water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and
(3) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the product to be prepared therefrom.
To impart good chemical durability to papers, boards, fibers, films, and coatings derived from the gels, those bodies will be contacted with a source of large cations, frequently K.sup.+ ions. This causes an ion exchange reaction to take place between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals.
U.S. Pat. No. 4,239,519 is primarily concerned with use of glass-ceramic type materials to produce crystal-containing gels. However, earlier work, as reported by the Bureau of Mines in Bulletin 647, Fluorine Micas, pages 236-242 (1969), involved sintering and recrystallizing a batch composed of raw materials such as talc, silica, magnesia, and fluorides to produce a water-swelling fluormica that was used in making paper.